The conventional automatic sprinkler head is connected to a water line and includes a body or frame that has an outlet orifice which is normally closed by a cap, and the cap is held in the closed position by a lever assembly which includes a low melting point fusible element. When the ambient temperature is increased to a predetermined level, the element will melt, releasing the lever assembly to open the orifice and discharge the water.
In residential dwellings and office buildings, it is often desired to utilize a sprinkler head that is located above the ceiling so that the operative parts are not exposed to view. In some cases, the sprinkler head is mounted within a recessed cup in the ceiling, and while the sprinkler head is recessed within the ceiling, the operative parts are not concealed.
In other instances, the sprinkler head is concealed within the ceiling by a decorative plate which is mounted flush against the ceiling so that none of the operative parts are visible.
In some concealed sprinkler head installations, such as disclosed in U.S. Pat Nos. 3,633,676, 3,714,989 and 3,756,321, the decorative plate is attached to the sprinkler head by a fusible material and when the sprinkler head is exposed to an elevated temperature, the fusible material will melt to release the decorative plate. Subsequently, the fusible element of the lever assembly will melt to release the lever assembly and open the valve cap. With sprinkler heads of this type, as used in the past, the fusible element associated with the lever assembly has been located a substantial distance above the lower surface of the ceiling and as a result the response rate of this type of sprinkler head has been relatively slow. In an attempt to increase the response rate, heat transfer fins or ribbons, such as disclosed in U.S. Pat. No. 3,756,321, have been associated with the lever assembly, and on release of the decorative plate, the fins drop down below the ceiling level in an attempt to increase the rate of heat transfer to the fusible element associated with the lever assembly.
In order to properly position the decorative plate of the concealed sprinkler head with respect to the ceiling, the valve body of the sprinkler head must be installed a precise distance from the lower surface of the ceiling. Concealed sprinkler heads, as used in the past, have had minimum provisions for adjustment, with the result that if the critical distance between the valve body and the ceiling was not maintained, the decorative plate of the sprinkler head could not be installed flush with the ceiling.